JPH0448683B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention automatically detects vertical tears that occur during operation of a conveyor belt used for transporting ore, lime, coal, etc. without contacting the belt. Regarding equipment.

Conventional technology and problems In conveyor belts that transport ore, lime, coal, etc., vertical cracks may occur due to the sharp edges of the ore, etc. The tear develops over the entire length of the belt, not only hindering the conveying function of the conveyor in question, but also
This makes the entire belt unusable.
Therefore, it is desirable to detect and repair longitudinal tears as soon as possible, but it is impossible to constantly monitor longitudinal tears with the naked eye in belts that are several hundred meters or more in length. Therefore, there is a need for a device that automatically detects vertical tears in conveyor belts, and various devices have been developed and devised in the past.

As a typical example, as described in Japanese Utility Model Publication No. 44-4180, a loop coil is buried in a conveyor belt, a detection coil is placed directly above the passage of the belt, and the effective inductance between the terminals of this detection coil is There are things that detect changes. Methods for detecting changes in the effective inductance L include a method in which the detection coil is inserted into one side of the bridge and the change in L is extracted as bridge unbalance, and a method in which the detection coil is used as an inductor coil of an oscillation circuit. There is a method of extracting the change in L as a change in the oscillation frequency.

However, when this method is applied to a conveyor belt with embedded reinforcing steel cords,
When the distance between the detection coil and the belt changes, the effective inductance also changes, generating an erroneous signal.
In general, conveyor belts frequently experience vertical vibrations and lateral vibrations during operation, and therefore, if the conventional method is applied to a conveyor belt with embedded reinforcing steel cords, it will generate many false signals. Therefore, it cannot be put to practical use. Furthermore, even if the distance between the detection coil and the belt can be effectively kept constant using a copying roll device, etc., the effective inductance at the connection portion of the steel cords will be reduced due to the difference in the embedded density of the steel cords. changes, causing an erroneous signal to be emitted.

OBJECTS OF THE INVENTION Therefore, the present invention provides a method for detecting vertical tearing of a conveyor belt, particularly a conveyor belt in which reinforcing steel cords are embedded, without malfunction during the service life of the belt, and automatically generating an alarm. This is what we are trying to do.

Composition of the Invention The present invention provides an apparatus for detecting longitudinal tearing of a conveyor belt, including a plurality of loop coils extending in the width direction of the belt and embedded at predetermined intervals in the longitudinal direction of the belt, and a device for electromagnetically coupling with the loop coils. a detection coil arranged opposite to the belt; a circuit connected to the detection coil to detect changes in effective reactance and effective resistance of the coil; and a circuit connected to the circuit to detect changes in effective reactance and resistance of the coil; This is characterized by comprising a circuit that rotates the phase so that the impedance change characteristic when facing a part other than the normal loop coil coincides with the reactance axis.This will be explained in detail below with reference to the drawings. .

Embodiment of the Invention Fig. 1 shows a conveyor belt equipped with a reinforcing steel cord and a loop coil for vertical tear detection, 10 is the belt made of rubber, 12 is the steel cord, and 14 is the loop coil. . A is a schematic plan view, and b is a cross-sectional view of the same. As shown in cross-sectional view b, the steel cord 12 and the loop coil 14 are buried in different layers, and the former is a belt for carrying cargo such as ore. the front side, and the latter on the back side of the belt. A plurality of steel cords 12 extend linearly in the longitudinal direction of the belt, and are arranged at approximately equal intervals in the width direction of the belt. Loop coil 14
is a one-turn or multiple-turn short-circuit coil, the winding axis of which is oriented perpendicular to the belt surface, and the rectangular coil extends across almost the entire width of the belt.
Although only one loop coil 14 is shown in FIG. 1, it is actually arranged at a predetermined pitch (for example,
30m) and are buried in large numbers. The reinforcing steel cord 12 and the loop coil 14 are electrically insulated.

FIG. 2 shows a state in which a baggage 16 is conveyed by such a belt conveyor 10. 18 and 20 are pulleys. 22 is a detection end equipped with a detection coil,
This detection coil serves as the primary winding of the transformer, and the loop coil serves as the secondary winding of the same transformer, and disconnection of the loop coil due to longitudinal tearing of the belt can be detected from changes in the impedance of the detection coil (effective resistance component R and effective reactance component It is detected as a change in the vector.

If a change in the impedance of the detection coil is detected as a change in the magnitude and/or direction of a vector consisting of an R component and an X component, it is possible to accurately detect loop coil breakage and hence longitudinal belt tearing. That is, clearly different vector changes appear when the detection coil faces part A where the loop coil of the belt is buried and when it faces part B where only the reinforcing steel cord is buried. Furthermore, if the loop coil is disconnected, the vector at that time will be almost the same as the vector of portion B.

FIG. 4 shows impedance changes of the detection coil measured by specifying the measurement frequency and the dimensions of the loop coil and steel cord. The vertical axis shows the reactance change ΔX, the horizontal axis shows the resistance change ΔR, and V ₁ ~
V ₅ is the impedance change of the detection coil measured at the loop coil section. V ₁ is when the distance between the detection coil and belt is 60 mm, V ₂ is 50 mm, V ₃ is 40 mm, V ₄ is 30 mm, V ₅
is for the case of 20 mm, and a larger impedance change is observed as the distance becomes smaller. The distance between the detection coil and the belt is related to the magnitude of the vectors, but not to the phase angle (orientation);
V ₁ , V ₂ , . . . are on the straight line C1. Straight line C2 represents the impedance change when the detection coil faces only the reinforcing steel cord of the belt.
In addition, straight line C3 shows the impedance change when the detection coil faces the disconnected loop coil,
As is clear from the figure, these are almost the same and are clearly different from that of the normal loop coil section C1. Similarly, if the distance between the detection coil and the belt differs, the magnitude of the vector changes, but the phase angle remains the same. The dotted lines are V ₁ , V ₂ ,... on C2, C3
...Indicates the corresponding position.

Therefore, by rotating each vector all at once, we can create a straight line C2.
If it is made to coincide with the ΔX axis, it can be said that when the ΔR component appears, it is when the detection coil faces a normal loop coil. The ΔR component varies depending on the distance between the detection coil and the belt (V ₁ ~
V ₅ ), but if a threshold value is set appropriately according to the possible intervals and it is determined whether a ΔR greater than that value is detected, the change in the interval can be ignored.

As shown in FIG. 3, the steel cords for reinforcing the belt are interlocked over a predetermined length at the connecting portion C, and the embedded density is high. Therefore, simple detection of effective inductance may result in erroneous detection in this part, but the present invention, which treats it as a vector, does not cause such erroneous detection. That is, the impedance of the detection coil is also on the straight line C2 in FIG. 4 even in this connecting portion C, and there is almost no change in the phase angle except for a slight increase in magnitude. Therefore, if the above-described phase rotation is performed, no ΔR component will be generated at the connection portion C, and no signal will be generated.

FIG. 5 shows an embodiment circuit of the present invention. 24 is the above detection coil, 26 is an AC power supply, 28 is a constant current circuit for driving the detection coil 24 with a constant current, 3
0 is a high input impedance buffer, and 32 is a phase shifter that generates reference signals S1 and S2 having a phase difference of 90 degrees. Also, 34 is a cancellation circuit 36
38 is an amplifier, 40 and 42 are phase detectors, and 44 is a phase rotation circuit.

When an alternating current of constant amplitude is supplied to the detection coil 24 by the constant current circuit 28, a voltage V proportional to the impedance Z of the coil appears across the coil 24 (because V=IZ and I=constant).
Since this voltage consists of a fixed component and a varying component, the fixed component is generated in a circuit 34, added to a circuit 36, the fixed component is removed by the circuit, only the varying component is taken out, and this is amplified by an amplifier 38. do. This is to avoid saturation of the amplifier 38 if the fixed portion is included in the amplification. The amplified voltage changes are reference voltages S1 and S2 with a 90° phase difference.
Phase detection is performed by the detectors 40 and 42 to which the voltage is added, and a resistance change ΔR and a reactance change ΔX are output. These ΔR and ΔX are the phase rotation circuit 4
In addition to step 4, processing is performed to align the aforementioned straight line C2 with the ΔX axis. ΔX, ΔR subjected to such processing
Of these, ΔR or it is checked using a threshold value Vth, and the signal equal to or greater than the threshold value Vth is taken out as an output signal ΔR'. This is a signal indicating normal loop coil detection as described above.

FIG. 6 shows another embodiment of the invention. 46 is a floating transformer whose primary winding is connected to the above-mentioned AC power supply 26, and whose secondary winding is connected to the detection coil 2.
4. energize the bridge 54 consisting of the dummy coil 48 and resistors 50 and 52; This bridge 54 is
When the detection coil 24 faces the non-loop coil portion of the belt, each side is adjusted so as to be balanced, and the input terminal of the amplifier 38 is connected to the detection terminal of this bridge to amplify the bridge unbalanced voltage. . As can be easily inferred from the above explanation, this bridge 54 becomes unbalanced only when the detection coil 24 faces the normal loop coil 14, and the unbalanced voltage includes only the variation and does not include the fixed voltage. The cancellation circuit 36 shown in FIG. 5 is not necessary. The components after the amplifier 38 are the same as those shown in FIG.

According to this circuit, disconnection of the loop coil and, therefore, longitudinal tearing of the belt can be detected reliably. Note that the detection output of this detection circuit is that when a loop coil is disconnected, the event pulse ΔR', which indicates the presence of a loop coil, is no longer generated, so this alone is not sufficient for vertical tear alarms, and for example, when a loop coil is disconnected, It is necessary to issue a loop coil breakage or vertical belt tear alarm on the condition that there is no event pulse even if this pulse occurs. However, such means can be constructed as appropriate and any known means can be used. For example, a disc provided with a light transmission hole is connected to a belt drive pulley, and when the detection coil faces a loop coil on the belt, light enters the light receiving element through the light transmission hole, and the light is incident on the light receiving element through the light transmission hole. One example is to set the output as a loop coil detection output, add this to one input of an AND gate, and add an inverted signal of the output ΔR' of the circuit 44 to the other input. If the belt is stretched and slack, it may be detected by the disc mentioned above and may be misaligned. To prevent this, operate a one-shot multi, etc. to generate a pulse of an appropriate width (window pulse), and use the AND gate to generate a pulse of an appropriate width (window pulse). This can be solved by opening the AND gate over an appropriate width before and after the expected position of the loop coil. It is also possible to directly detect the loop coil position by embedding a magnet in the belt at or near the loop coil position and detecting this with a second detection coil.

When the loop coil 14 makes electrical contact with the steel cord 12, the impedance of the detection coil changes randomly. Therefore, it is advisable to insulate both. In addition, the loop coil 14 is preferably laid on the belt 10 so as to directly face the detection coil 24, and when the steel cord 12 is inserted between them, the steel cord performs an electromagnetic shielding function, and the loop coil detection output is reduced. Become.

Effects of the Invention As explained above, according to the present invention, it is possible to reliably detect vertical tearing of a belt conveyor with a built-in steel cord, and it is extremely effective. Of course, the present invention may be applied to a belt conveyor that does not have a built-in steel cord, and no problem will occur even if this is done.

[Brief explanation of drawings]

Figures 1 to 3 are explanatory diagrams of the conveyor belt, Figure 4 is an impedance change characteristic diagram of the detection coil,
FIGS. 5 and 6 are block diagrams showing circuits according to an embodiment of the present invention. In the drawings, 10 is a conveyor belt, 12 is a steel cord, 14 is a loop coil, 24 is a detection coil, 30, 36, 38, 40, 42 or 54,
38, 40, 42 are detection circuits for ΔR and ΔX, 44
is a phase rotation circuit.

Claims (1)

[Claims] 1. A device for detecting longitudinal tearing of a conveyor belt, comprising: a plurality of loop coils extending in the width direction of the belt and embedded at predetermined intervals in the longitudinal direction of the belt, and electromagnetically coupled to the loop coils. a detection coil disposed opposite to the belt; a circuit connected to the detection coil to detect changes in effective reactance and effective resistance of the coil; and a circuit connected to the circuit to transmit its output to the belt. A belt longitudinal tear detection device comprising: a circuit for phase rotation so that impedance change characteristics when facing a portion other than a normal loop coil coincide with a reactance axis.